1. Field of the Invention
The present invention relates to an optical element which limits propagation of light that obliquely propagate with respect to a surface and also relates to an illuminating device, display device and electronic device using the optical element.
2. Description of the Related Art
There are cases in which the user does not want other people to peep at the display screen of a user's display device. For this purpose, use of a film-like optical element that limits propagation of light obliquely incident on a surface has been known. This film-like optical element is called “microlouver”.
As shown in FIG. 1, microlouver 200 includes light absorbing layers 202 and transparent layers 203 arranged alternately. When this illustrated microlouver 200 is laid over the display surface of a display device, propagation of light obliquely outgoing from the display surface is limited, so that the displayed image cannot be seen from oblique positions.
Microlouver 200, as described above, limits propagation of light in the direction that intersects light absorbing layers 202, but does not limit propagation of light in the direction parallel to light absorbing layers 202. More specifically, a microlouver is generally arranged on the display surface of a display device such that light absorbing layers 202 are arrayed in the left-to-Right direction. Accordingly, it is possible to prevent the displayed image from being seen from oblique right positions or oblique left positions (to be referred to as oblique right and left positions). However, in this case, emission of light in oblique upper and oblique lower directions (to be referred to as oblique upper and lower direction) from the display surface will not be limited. As a result, the displayed image is seen from oblique positions above and below. To deal with this, there are cases in which two sheets of microlouvers are used in order to limit emission of light to oblique upper and lower directions in addition to limit emission of light to oblique left and right positions.
Further details on the microlouver are disclosed in Japanese Patent Application Laid-open S50-92751 (lines 4-8 in the lower left column on page 2, FIG. 3).
However, use of two sheets of microlouvers increases cost. Further, assembly of two sheets of microlouvers into an illuminating device or display device makes the illuminating device or display device thicker.